So I have enco knee mill that has servos for the X and Y. It is no longer used and the controller is fried. I have retrofitted 2 mills in the past so think I want to turn this into a 3D printer.
So here’s where I want some feed back.
I know I could just buy one but this is more fun:-)
I recommend the E3D hot end. Then you have to decide what extruder. Are you going Bowden or direct drive? The choice will tell you how much power you need and that will determine what you can get away with, which will size the rest of your parts. A direct drive unit will have better filament feed over a broader range of materials but will be heavier and harder to control the position of than a Bowden unit.
Right now my preference for slicers is Cura. It seems to be the best supported, though Slic3r is also good. There are a variety of others but I haven’t used them yet. Determine your control software and see if that will restrict or expand the list of slicers.
If you are going to have a heated bed and use ABS, yes, enclose the build area. If you are going to print PLA or PET, you don’t need to enclose it. If you want to get into exotics, you should enclose it for fume control and thermal control with a filter system.
Thanks! Think I will go with the direct drive as weight really isn’t an issue because the mill is so stout and I will have the z geared way down. I’ll check out those programs.
I’ll just chime in to agree with @ben1’s comments.
There are some fancy extruders you can get for doing multi-color. But fancy means more failure points in almost all cases. The E3D is well known and built.
I continue to use Slic3r, but also have Cura available in case I need something done and Slic3r fails at it.
And yeah… ABS needs an enclosed area, you want the whole part to cool at once. But PLA is best if it cools as much as possible upon deposition, so enclosing makes things work poorly (cannot bridge as far for example)
I like both Slic3r and Cura.
I used Slic3r for years with my Solidoodle 2 and it was a champ. Did everything I needed to do.
I’m new to Cura. I’ve only started using it with the arrival of my Monoprice 3D printer but it seems pretty good so far.
I’ve heard nothing but good things about the E3D hot end!
Great suggestions on the build. However, I would also suggest looking at Craftware for your slicing needs. Craftunique makes a really competitive (features) slicer. Even though it is proprietary to the Craftbot, it works with many different printer types. Great forum as well. Lots of help and price is free.
Is the mill going to be capable of the speeds you want in a printer (5000mm/min and up)? If so, at least you won’t have to worry about vibration as much 
Because you’ve got lots of structure available, I would recommend a traveling enclosure lid. More efficient, and keeps some heat away from things you don’t want so hot, like the extruder and hot-end fans.
“Is the mill going to be capable of the speeds you want in a printer (5000mm/min and up)?”
Good question, I know I can get 2500 out of it but 5000 might be a bit much cause of the mass.
Can you explain a “traveling enclosure”?
thanks
Non-3d-printer-having person here thinking out loud… maybe a “traveling enclosure” would make it unnecessary, but from what @jacobturner is saying above, it seems to me that to have the most flexible system possible you would want to have a quick-release or convertible enclosure?
Yep! Best of all worlds. Was planning to build one for the M2 with the Glowie.
(Temporarily on hold.) 
If the mill is already not working as a mill, it might be worth the time to take apart as much table as you can to lose mass – printing speed is really a big deal. (Or you might look into one of the big-nozzle heads, which let you pump out ridiculous amounts of plastic fairly quickly.)
For ABS I built an enclosure where the top rides up with the extruder, trapping most of the heated air below it. Reduces heating time and energy requirements a bit. But now I look at knee mill pictures I realize the Z travel is the other way, so the top of your enclosure would be fixed and the question would be whether the bottom could move. Oops.
Doors as enclosures is typically adequate. You also want a nozzle fan for PLA to get best results, and you absolutely do NOT want a nozzle fan for ABS to get any results at all.
E3 V6 hot end (and a real one, not a clone, lots of fakes - the US dealer is filastruder)
E3d titan exruder
Simplify 3D. Watch angus’ video on makers muse on YouTube with the slicer shootout.
Oh, sometimes you do (when you’re running really fast layers) but it has to be blowing pretty hot air.
So a recording of any political debate through a loud speaker into your 3d printing area?
I agree, the E3d hot end works well but I haven’t had great success with their titan hot end. I love and use simplify 3D.
The Jerome says he uses the KISSlicer, and its fill patterns for sparse internals are very strong and unlike other slicers, it doesn’t direct the hot end through plastic it’s already laid down.
I am running titans on my E3D BigBox and if you aren’t having good success make sure you didn’t get one of the mistake ones. A lot of people were complaining (me included) then they discovered a whole batch were made with the wrong tooth pattern, got the new ones sent out and this thing is rock solid…
Make sure your titan hob looks like the left, not right.
